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Relationship: 229

Title

A descriptive phrase which clearly defines the two KEs being considered and the sequential relationship between them (i.e., which is upstream, and which is downstream). More help

Binding of antagonist, NMDA receptors leads to Inhibition, NMDARs

Upstream event

The causing Key Event (KE) in a Key Event Relationship (KER). More help

Binding of antagonist, NMDA receptors

Downstream event

The responding Key Event (KE) in a Key Event Relationship (KER). More help

Inhibition, NMDARs

Key Event Relationship Overview

The utility of AOPs for regulatory application is defined, to a large extent, by the confidence and precision with which they facilitate extrapolation of data measured at low levels of biological organisation to predicted outcomes at higher levels of organisation and the extent to which they can link biological effect measurements to their specific causes.Within the AOP framework, the predictive relationships that facilitate extrapolation are represented by the KERs. Consequently, the overall WoE for an AOP is a reflection in part, of the level of confidence in the underlying series of KERs it encompasses. Therefore, describing the KERs in an AOP involves assembling and organising the types of information and evidence that defines the scientific basis for inferring the probable change in, or state of, a downstream KE from the known or measured state of an upstream KE. More help

AOPs Referencing Relationship

AOP Name	Adjacency	Weight of Evidence	Quantitative Understanding	Point of Contact	Author Status	OECD Status
Chronic binding of antagonist to N-methyl-D-aspartate receptors (NMDARs) during brain development induces impairment of learning and memory abilities	adjacent	High		Anna Price (send email)	Open for citation & comment	WPHA/WNT Endorsed
Chronic binding of antagonist to N-methyl-D-aspartate receptors (NMDARs) during brain development leads to neurodegeneration with impairment in learning and memory in aging	adjacent	High		Florianne Tschudi-Monnet (send email)	Open for citation & comment	WPHA/WNT Endorsed

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KER.In general, this will be dictated by the more restrictive of the two KEs being linked together by the KER. More help

Sex Applicability

An indication of the the relevant sex for this KER. More help

Life Stage Applicability

An indication of the the relevant life stage(s) for this KER. More help

Key Event Relationship Description

Provides a concise overview of the information given below as well as addressing details that aren’t inherent in the description of the KEs themselves. More help

It is well documented that prolonged/chronic antagonism of NMDARs triggers the downstream KE named inhibition of NMDARs. Shorter term binding to the same receptors may trigger different downstream KEs, such as up-regulation of the NMDARs, resulting in toxic increased influx of calcium and to cell death. Consequently, this information can be captured in other KERs and AOP.

Evidence Collection Strategy

Include a description of the approach for identification and assembly of the evidence base for the KER. For evidence identification, include, for example, a description of the sources and dates of information consulted including expert knowledge, databases searched and associated search terms/strings. Include also a description of study screening criteria and methodology, study quality assessment considerations, the data extraction strategy and links to any repositories/databases of relevant references.Tabular summaries and links to relevant supporting documentation are encouraged, wherever possible. More help

Evidence Supporting this KER

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help

Biological Plausibility

Addresses the biological rationale for a connection between KEupstream and KEdownstream. This field can also incorporate additional mechanistic details that help inform the relationship between KEs, this is useful when it is not practical/pragmatic to represent these details as separate KEs due to the difficulty or relative infrequency with which it is likely to be measured. More help

There is structural mechanistic understanding supporting the relationship between MIE (NMDARs, binding of antagonists) and KE (NMDARs, inhibition). Crystal structure studies are used to study the binding of antagonists/agonists to NMDA receptors. In case of NMDAR antagonists, the binding to the receptor causes LBD conformation changes which promote channel closure leading to reduced Ca+2 influx (Blanke and VanDongen, 2009). This lack of measurable ion flux is applied as an indication of NMDAR inhibition.

Empirical Evidence

Provides specific (citable) evidence that supports the idea of a change in the upstream KE (KEupstream) leading to, or being associated with, a subsequent change in the downstream KE (KEdownstream), assuming the perturbation of KEupstream is sufficient. More help

Include consideration of temporal concordance here

In slices of cerebellum derived from postnatal days 6-30 (PND 6-30) Sprague Dawley rats, 10 µM MK-801 completely blocked evoked NMDA excitatory postsynaptic currents (EPSCs) as it has been demonstrated by patch clamp technique (Rumbaugh and Vicini, 1999). The same technique has been employed in cortical slices from C57BL/6 mice of both genders and different age groups (P8-12, P21-28 or P45-90), showing that 1 µM APV and 50 nM NVP-AAM077 antagonise a similar amount of NMDA receptor current independently of the age (de Marchena et al., 2008).

Pb acts as a non-competitive, voltage independent antagonist of NMDAR. Pb action partially overlaps with that of zinc (Gavazzo et al., 2008)

Pb2+ has potent inhibitory effects on the NMDA receptor (Alkondon et al., 1990; Guilarte and Miceli, 1992; Guilarte, 1997; Gavazzo et al., 2001). In rat hippocampal neurons, Pb2+ (2.5-50 μM) inhibits NMDA-induced whole-cell and single-channel currents in a concentration-dependent manner, suggesting that Pb2+ can decrease the frequency of NMDA-induced channel activation (Alkondon et al., 1990). In the same study, they have examined the effect of Pb2+ on the binding of [3H]MK-801 to the rat brain hippocampal membranes and showed that Pb2+ inhibits the binding of [3H]-MK-801 in a concentration dependent manner with an IC50 value close to 7 µM (Alkondon et al., 1990). These inhibitory effects of Pb2+ on NMDA receptors activation appear to be age and brain region specific (Guilarte, 1997; Guilarte and Miceli, 1992). The Pb2+ IC50 is significantly lower in cortical membranes prepared from neonatal than from adult rats, whereas the hippocampus is more sensitive than the cerebral cortex since the Pb2+ IC50 is significantly lower in the hippocampus (Guilarte and Miceli, 1992). The number of [3H]-MK-801 binding sites associated with the high and low affinity sites of Pb2+ inhibition in the hippocampus of rats is increased as a function of age, peaking at PND 28 and 21 (Guilarte, 1997). High and low affinity Pb(2+)-sensitive [3H]-MK-801 binding sites have also been measured in the cerebral cortex during early development, but that has not been possible to evaluate after PND 14.

The developing brain is more sensitive than the adult brain to Pb2+-induced effects mediated through the NMDA receptor. Moreover, the hippocampus appears to be particularly vulnerable as in this brain structure NMDA receptors undergo subunit specific changes during developmental Pb2+ exposure (Guilarte and McGlothan, 1998). Exposure to Pb2+ during synaptogenesis causes decreased expression of hippocampal NR2A-subunit of NMDARs at synapses and increased targeting of NR2B-NMDARs to dendritic spines (without increased NR2B-NMDARs expression) (Nihei and Guilarte, 1999; Neal et al., 2011; Zhang et al., 2002).

Uncertainties and Inconsistencies

Addresses inconsistencies or uncertainties in the relationship including the identification of experimental details that may explain apparent deviations from the expected patterns of concordance. More help

Pb2+ has been found to produce either potentiation or inhibition depending on: a) the subunit composition of NMDA receptors, b) endogenous glutamate concentration and c) Pb2+ dosage. In case that the NMDA receptors are saturated by agonist, Pb2+ at low concentrations (<1 µM) acts as a positive modulator of agonist action at NR1b-2AC and NR1a-2AB subunit complexes, whereas at higher concentrations, Pb2+ it behaves as a potent inhibitor of all recombinant NMDA receptors tested and was least potent at NR1b-2AC (Omelchenko et al., 1996; 1997), meaning that Pb2+ is not always acting as NMDAR inhibitor but it can also behave as NMDAR activator under certain conditions.

As an alternative mechanism of toxicity, Pb was shown to cause oxidative stress. In addition, it has the ability to substitute other bivalent cations like Ca2+,Mg2+, Fe2+ and monovalent cations like Na+ (for review, see Flora et al., 2012)

Known modulating factors

This table captures specific information on the MF, its properties, how it affects the KER and respective references.1.) What is the modulating factor? Name the factor for which solid evidence exists that it influences this KER. Examples: age, sex, genotype, diet 2.) Details of this modulating factor. Specify which features of this MF are relevant for this KER. Examples: a specific age range or a specific biological age (defined by...); a specific gene mutation or variant, a specific nutrient (deficit or surplus); a sex-specific homone; a certain threshold value (e.g. serum levels of a chemical above...) 3.) Description of how this modulating factor affects this KER. Describe the provable modification of the KER (also quantitatively, if known). Examples: increase or decrease of the magnitude of effect (by a factor of...); change of the time-course of the effect (onset delay by...); alteration of the probability of the effect; increase or decrease of the sensitivity of the downstream effect (by a factor of...) 4.) Provision of supporting scientific evidence for an effect of this MF on this KER. Give a list of references. More help

Quantitative Understanding of the Linkage

Captures information that helps to define how much change in the upstream KE, and/or for how long, is needed to elicit a detectable and defined change in the downstream KE. More help

Is it known how much change in the first event is needed to impact the second? Are there known modulators of the response-response relationships? Are there models or extrapolation approaches that help describe those relationships?

To predict how potent an antagonist can be, the half maximal inhibition concentrations (IC50) and the half maximal effective concentration (EC50) of glutamate/glycine induced currents is measured in NMDA receptors from brain slices and cells or in recombinantly expressed receptors. Traynelis et al. 2010 summarised the IC50 values for competitive, noncompetitive and uncompetitive antagonists in different subunits of NMDA receptors. The inhibitory effect (efficacy) of antagonists on NMDA receptors has been found to be dependent on:

-the type of subunits that form the NMDA receptors depending on the developmental stage -the chemical structure of the antagonists

-the binding site of receptor that the antagonists prefer

-how tightly an antagonist binds to the receptor (affinity)

At CA3-CA1 synapses, NMDARs are largely composed of NR1 (NMDA receptor subunit 1)-NR2A or NR1-NR2B containing subunits. Recent, but controversial, evidence has correlated NR1-NR2A receptors with the induction of LTP and NR1-NR2B receptors with LTD. However, LTP can be induced by activation of either subtype of NMDAR and the ratio of NR2A:NR2B receptors has been proposed as an alternative determinant of the direction of synaptic plasticity (Mac Donald et al., 2006).

Pb2+: Although the NR2 subunits have different Zn2+ binding sites i.e. the NR2A-NMDAR binds Zn2+ at a high-affinity site (nM affinity) while the NR2B-NMDAR binds Zn2+ with lower affinity (µM range); the Pb2+ IC50 for wild type NR2A-NMDARs was reported to be 1.3 µM, while the Pb2+ IC50 of wild type NR2B-NMDARs was 1.2 µM (Gavazzo et al., 2008). Similar findings were published by Lasley and Gilbert (1999) using cortical neurons from adult rats. The IC50 for Pb2+ ranged from 1.52 to 4.86 µM, with the ranking of Pb2+ potency in inhibition of NMDA receptor subunits to be NR1b-2A>NR1b-2C>NR1b-2D>NR1b-2AC after experiments that have been conducted in Xenopus oocytes injected with cRNAs for different combinations of NMDA receptor subunits (Omelchenko et al., 1997).

Response-response Relationship

Provides sources of data that define the response-response relationships between the KEs. More help

Time-scale

Information regarding the approximate time-scale of the changes in KEdownstream relative to changes in KEupstream (i.e., do effects on KEdownstream lag those on KEupstream by seconds, minutes, hours, or days?). More help

Known Feedforward/Feedback loops influencing this KER

Define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits. More help

Domain of Applicability

A free-text section of the KER description that the developers can use to explain their rationale for the taxonomic, life stage, or sex applicability structured terms. More help

The biophysical properties of rat and human receptors have been mostly assessed through recombinant studies, whereas the pharmacological properties of rat and human NMDA receptors have not been fully explored and compared yet (Hedegaard et al., 2012). Mean channel open times for human NMDA receptor subtypes in recombinant protein studies are similar to those of the corresponding rat NMDA receptor subtypes. However, mean single-channel conductances for human NMDA receptor subtypes appear lower than those of the corresponding rat NMDA receptor subtypes. Regarding pharmacological properties of the receptors, the differences were less than 2-fold and were not observed at the same subtypes for all the antagonists tested, suggesting that the molecular pharmacology of NMDA receptor is conserved between human and rat, although some inter-species differences are seen in IC50 values using two-electrode voltage-clamp recordings (Hedegaard et al., 2012),

References

List of the literature that was cited for this KER description. More help

Alkondon M, Costa AC, Radhakrishnan V, Aronstam RS, Albuquerque EX. (1990) Selective blockade of NMDA-activated channel currents may be implicated in learning deficits caused by lead. FEBS Lett. 261: 124-130.

Blanke ML, VanDongen AMJ. (2009) Activation Mechanisms of the NMDA Receptor. In: Van Dongen AM, editor. Biology of the NMDA Receptor. Boca Raton (FL): CRC Press; Chapter 13. Available from: http://www.ncbi.nlm.nih.gov/books/NBK5274/

de Marchena J, Roberts AC, Middlebrooks PG, Valakh V, Yashiro K, Wilfley LR, Philpot BD. (2008) NMDA receptor antagonists reveal age-dependent differences in the properties of visual cortical plasticity. J Neurophysiol. 100: 1936-1948.

Flora G, Gupta D, Tiwari A. 2012. Toxicity of lead: A review with recent updates. Interdisciplinary toxicology 5(2): 47-58.

Gavazzo P, Gazzoli A, Mazzolini M, Marchetti C. (2001) Lead inhibition of NMDA channels in native and recombinant receptors. NeuroReport. 12: 3121-3125.

Gavazzo P, Zanardi I, Baranowska-Bosiacka I, Marchetti C. (2008) Molecular determinants of Pb2+ interaction with NMDA receptor channels. Neurochem Int. 52: 329-337.

Guilarte TR, Miceli RC. (1992) Age-dependent effects of lead on [3H]-MK-801 binding to the NMDA receptor-gated ionophore: In vitro and in vivo studies. Neurosci Lett. 148: 27-30.

Guilarte TR. (1997) Pb2+ Inhibits Nmda Receptor Function at High and Low Affinity Sites: Developmental and Regional Brain Expression. Neurotoxicology 18: 43-51.

Guilarte TR, McGlothan JL. (1998) Hippocampal NMDA Receptor mRNA Undergoes Subunit Specific Changes During Developmental Lead Exposure. Brain Res. 790: 98-107.

Hedegaard MK, Hansen KB, Andersen KT, Bräuner-Osborne H, Traynelis SF. (2012) Molecular pharmacology of human NMDA receptors. Neurochem Int. 61: 601-609.

Lasley SM, Gilbert ME. (1999) Lead inhibits the rat N-methyl-d-aspartate receptor channel by binding to a site distinct from the zinc allosteric site. Toxicol Appl Pharmacol. 159: 224-233.

MacDonald JF, Jackson MF, Beazely MA. (2006) Hippocampal long-term synaptic plasticity and signal amplification of NMDA receptors. Crit Rev Neurobiol. 18: 71-84.

Neal AP, Worley PF, Guilarte TR. (2011) Lead exposure during synaptogenesis alters NMDA receptor targeting via NMDA receptor inhibition. Neurotoxicology 32: 281-289.

Nihei MK, Guilarte TR. (1999) NMDAR-2A subunit protein expression is reduced in the hippocampus of rats exposed to Pb2+ during development. Brain Res Mol Brain Res. 66: 42-49.

Omelchenko IA, Nelson CS, Marino JL., Allen CN. (1996). The sensitivity of N-methyl-d-aspartate receptors to lead inhibition is dependent on the receptor subunit composition. J Pharmacol Exp Ther. 278: 15-20.

Omelchenko IA, Nelson CS, Allen CN. (1997) Lead inhibition of N-Methyl-D-aspartate receptors containing NR2A, NR2C and NR2D subunits. J Pharmacol Exp Ther. 282: 1458-1464.

Rumbaugh G, Vicini S. (1999) Distinct Synaptic and Extrasynaptic NMDA Receptors in Developing Cerebellar Granule Neurons. J Neurosc. 19: 10603-10610.

Traynelis S, Wollmuth LP, McBain CJ, Menniti FS, Vance KM, Ogden KK, Hansen KB, Yuan H, Myers SJ, Dingledine R. (2010) Glutamate receptor ion channels: structure, regulation, and function. Pharmacol Rev. 62: 405-496.

Zhang XY, Liu AP, Ruan DY, Liu J. (2002) Effect of developmental lead exposure on the expression of specific NMDA receptor subunit mRNAs in the hippocampus of neonatal rats by digoxigenin-labeled in situ hybridization histochemistry. Neurotox Teratol 24: 149-160.